Nitric oxide (NO) is involved in many cellular functions, some of which may appear to be paradoxical. For example, in some settings elevated NO levels are associated with enhanced cell growth, while in others high concentrations of NO reduce cellular proliferation. NO is synthesized via the activity of one of three forms of nitric oxide synthase (NOS): neuronal NOS (nNOS or NOS 1); inducible NOS (iNOS or NOS 2); and endothelial NOS (eNOS or NOS 3). As implied by its name, iNOS is induced by a variety of external stimuli, including cytokines, immune complexes, lipopolysaccharides, and other pro-inflammatory molecules. Changes in NO have been described in autoimmune disorders, including inflammatory arthritis in animals and in humans. Many of the molecules that upregulate iNOS also stimulate the activity of the cyclooxygenase (COX) family of enzymes. These enzymes are responsible for the synthesis of prostaglandins (PGs) from arachidonic acid. The inducible isoform of the enzyme, COX-2, also has been implicated in inflammatory arthritis. NO can modulate COX activity, and PGs can modulate NOS activity in this and other conditions. Drugs that act as COX inhibitors have been developed, including the original nonsteroidal anti-inflammatory drugs (NSAIDs) that nonspecifically block both forms of the COX enzymes, and the newer, more specific COX-2 inhibitors. While COX-2 inhibitors have been shown to alter iNOS activity in some settings, little is known about their effects on iNOS in inflammatory arthritis. Because of the similarities in the stimuli that induce COX-2 and iNOS and because of the other interactions between these molecules, it seems likely that COX-2 inhibitors might alter iNOS activity as well. This proposal will examine some of the interrelationships between NOS and COX in inflammatory arthritis by studying the effects of nonspecific and selective COX inhibitors in mice with different NOS genetic backgrounds, thus permitting the dissection of the roles of iNOS, eNOS, and COX in the severity of inflammation. Additionally, changes in serum proteins will be explored using the tools of proteomic analysis to permit the identification of potential biomarkers for arthritis progression and therapeutic response and as part of an effort to understand the underlying mechanisms-involved in COX and NOS interactions that may account for some of the seemingly paradoxical effects of NO on the inflammatory process.